Heat oven to 425 degrees F.
In a small bowl, whisk together vinegar, mustard, paprika, 1/4 tsp of the salt and 1/8 tsp of the pepper. While whisking, add oil in a stream.
Toss potatoes with 2 tbsp of the dressing and spread onto a rimmed baking sheet. Sprinkle paprika on cut side of onion and add to pan, cut side up. Roast at 425° for 20 minutes.
Stir potatoes and push to one side of the pan. Remove onion to a cutting board. Toss asparagus with 1 tbsp of the remaining dressing and add to pan. Continue to roast at 425 degrees for 20 minutes.
Meanwhile, toss salmon with remaining 2 tbsp dressing. Cut onion into 4 wedges, then cut wedges in half. Thread eight 6- to 8-inch skewers with salmon, onion and cherry tomatoes. Season with 1/4 tsp salt and 1/8 tsp pepper.
Remove potatoes and asparagus from oven. Season with remaining 1/4 tsp salt and 1/4 tsp pepper. Turn oven temperature up to broil.
Broil skewers, 4 inches from heat, for 5 minutes, turning once. Serve skewers over roasted vegetables.
When serving expensive fish or meat, stretch your dollar by making kabobs.